Method and structure for non-linear optics

ABSTRACT

A compound for non-linear optics for use at 350 nm and below. The compound includes a material for non-linear optics comprising A x M (1-x) Al 3 B 4 O 12 . x is larger than or equal to zero and smaller than or equal to 0.1, A is selected from a group consisting of Sc, Y, La, Yb, and Lu, and M is selected from a group consisting of Sc, Y, La, Yb, and Lu. The compound is free from a molybdenum bearing impurity of at least 1000 parts per million.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.11/107,367, filed Apr. 14, 2005, now abandoned, which claims priority toU.S. Provisional Application No. 60/562,881 filed Apr. 16, 2004. U.S.Provisional Application No. 60/562,881 is incorporated by referenceherein. U.S. Provisional Application No. 60/562,626 is not incorporatedby reference.

STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER FEDERALLY SPONSOREDRESEARCH OR DEVELOPMENT

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REFERENCE TO A “SEQUENCE LISTING,” A TABLE, OR A COMPUTER PROGRAMLISTING APPENDIX SUBMITTED ON A COMPACT DISK

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BACKGROUND OF THE INVENTION

The present invention relates generally to certain compounds havingoptical properties. More particularly, as an example, the inventionprovides a specific compound comprising A_(x)M_((1-x))Al₃B₄O₁₂ for usewith selected wavelengths of electromagnetic radiation. x is larger thanor equal to zero and smaller than or equal to 0.1, A is selected from agroup consisting of Sc, Y, La, Yb, and Lu, and M is selected from agroup consisting of Sc, Y, La, Yb, and Lu. Merely by way of example, thecompound is useful for electromagnetic radiation having a wavelength of350 nm and less, but it would be recognized that the invention has amuch broader range of applicability.

Nonlinear optical (NLO) materials are unusual in that they affect theproperties of light. A well-known example is the polarization of lightby certain materials, such as when materials rotate the polarizationvectors of absorbed light. If the effect on the polarization vector bythe absorbed light is linear, then light emitted by the material has thesame frequency as the absorbed light. NLO materials affect thepolarization vector of the absorbed light in a nonlinear manner. As aresult, the frequency of the light emitted by a nonlinear opticalmaterial is affected.

For example, when a beam of coherent light of a given frequency, such asproduced by a laser, propagates through a properly oriented NLO crystalhaving non-zero components of the second order polarizability tensor,the crystal will generate light at a different frequency, thus extendingthe useful frequency range of the laser. Generation of this light can beascribed to processes such as sum-frequency generation (SFG),difference-frequency generation (DFG) and optical parametricamplification (OPA). Devices using NLO crystals include, but are notlimited to up and down frequency converters, optical parametricoscillators, optical rectifiers, and optical switches.

Frequency generation in NLO materials is usually an important effect.For example, two monochromatic electromagnetic waves with frequencies ω₁and ω₂ propagating through a properly oriented NLO crystal can result ingeneration of light at a variety of frequencies. Mechanisms defining thefrequency of light using these two separate frequencies aresum-frequency generation (SFG) and difference-frequency generation(DFG). SFG is a process where light of frequency ω₃ is generated as thesum of the two incident frequencies, ω₃=ω₁+ω₂. In other words, SFG isuseful for converting long wavelength light to shorter wavelength light(e.g. near infrared to visible, or visible to ultraviolet). A specialcase of sum-frequency generation is second-harmonic generation (SHG)where ω₃=2ω₁, which is satisfied when the incident frequencies areequal, ω₁=ω₂. DFG is a process where light of frequency ω₄ is generatedas the difference of the incident frequencies ω₄=ω₁−ω₂. DFG is usefulfor converting shorter wavelength light to longer wavelength light (e.g.visible to infrared). A special case of DFG is when ω₁=ω₂, hence ω₄=0,which is known as optical rectification. Optical parametric oscillation(OPO) is also a form of DFG and is used to produce light at tunablefrequencies.

The conversion efficiency of an NLO crystal for a particular applicationis dependent on a number of factors that include, but are not limitedto: the effective nonlinearity of the crystal (picometers/volt [pm/V]),birefringence (Δn, where n is a refractive index), phase-matchingconditions (Type I, Type II, non-critical, quasi, or critical), angularacceptance angle (radian-cm), temperature acceptance (.degree. K-cm),walk-off (radian), temperature dependent change in refractive index(dn/dT), optical transparency range (nm), and the optical damagethreshold (W/cm²). Desirable NLO crystals should posses an optimumcombination of the above properties as defined by the specificapplication.

Borate crystals form a large group of inorganic NLO materials used invarious applications, such as laser-based manufacturing, medicine,hardware and instrumentation, communications, and research studies. Betabarium borate (BBO: β-BaB₂O₄), lithium triborate (LBO: LiB₃O₅), andcesium lithium borate (CLBO: CsLi(B₃O₅)₂) are examples of borate-basedNLO crystals developed in recent years that are being used widely as NLOdevices, especially in high power applications. Select propertiessuitable for generation of laser light from the mid-infrared to theultraviolet for these crystals are listed in Table 1.

TABLE 1 Commercially Available NLO Materials and Properties PROPERTY BBOLBO CLBO D_(eff) (pm/V) 2.2 0.8 0.9 Optical Transmission (nm) 190-3500160-2600 180-2750 Angular Acceptance (mrad-cm) 0.8 6.5 0.6 TemperatureAcceptance (K-cm) 55 7.5 2.5 Walk-off Angle (deg.) 3 0.6 1.8 DamageThreshold (GW/cm²) 5 10 10 Crystal Growth Properties flux or congr. fluxcongruent

BBO has a favorable non-linearity (about 2.2 pm/V), transparency between190 nm and 3500 nm, significant birefringence (necessary for phasematching), and a high damage threshold (5 GW/cm², 1064 nm, 0.1 ns pulsewidth). However, its high birefringence creates a relatively smallangular acceptance that can limit conversion efficiencies and laser beamquality. The crystal is relatively difficult to grow to large sizes andis somewhat hygroscopic.

LBO exhibits optical transparency throughout the visible electromagneticspectrum, extending well into the ultraviolet (absorptionedge.congruent. 160 nm), and possesses a high damage threshold (10GW/cm², 1064 nm, 0.1 ns pulse width). However, it has insufficientintrinsic birefringence for phase matching to generate deep UVradiation. Furthermore, LBO melts incongruently and must be prepared byflux-assisted crystal growth methods. This limits production efficiencythat leads to small crystals and higher production costs.

CLBO appears capable of producing UV light due to a combination of highnonlinearity and sufficient birefringence. The crystal can also bemanufactured to relatively large dimensions. However, the crystalusually is exceedingly moisture sensitive and often invariably sorbswater from the air; hence, extreme care usually must be taken to manageenvironmental moisture to prevent hydration stresses and possiblecrystal destruction.

In 1981 a crystal called NYAB [Nd_(x)Y_((1-x))Al₃B₄O₁₂] was reported inthe USSR. A laser self-frequency-doubling effect from 1320 nm to 660 nmwas realized in a Nd_(0.2)Y_(0.8)Al₃B₄O₁₂ crystal, but it was found thatintrinsic crystal absorption at the second harmonic limited practicaluse of laser self-frequency-doubling from 1060 nm to 530 nm.

Years later several institutes in China succeeded in improving thecrystal growing process and obtained NYAB crystals of good opticalquality and reasonable size. Lu et al. developed a multi-functionalcrystal Nd_(x)Y_((1-x))Al₃B₄O₁₂ with effective laserself-frequency-doubling conversion. The Nd³⁺ doped laser gain crystalwas pumped with a dye laser, with laser emission at 1060 nm that wasthen converted to 530 nm within itself (see FIG. 2 of Lu et al., ChinesePhys. Lett. Vol. 3, No. 9 (1986)). NYAB has since been used as aresearch crystal that often is useful only in the visible spectrum.Recent work with Yb-doped YAB as a self-doubling laser gain materialfollows the same path as NYAB with small alterations in operationallaser efficiency and wavelengths. Laser light is generated within thecrystal and self-doubled into green 520 nm. (see Dekker et al., JOSA B,Vol. 22, No. 2 (2005) 378-384). Again, its operation and the historicmethod of preparation limit its use to the visible and infrared. Hence,it is highly desirable to improve techniques for this family ofcompounds that enable optical function down into the ultraviolet.

Hence, it is highly desirable to improve techniques for opticalcompounds.

BRIEF SUMMARY OF THE INVENTION

The present invention relates generally to certain compounds havingoptical properties. More particularly, as an example, the inventionprovides a specific compound comprising A_(x)M_((1-x))Al₃B₄O₁₂ for usewith selected wavelengths of electromagnetic radiation. x is larger thanor equal to zero and smaller than or equal to 0.1, A is selected from agroup consisting of Sc, Y, La, Yb, and Lu, and M is selected from agroup consisting of Sc, Y, La, Yb, and Lu. Merely by way of example, thecompound is useful for electromagnetic radiation having a wavelength of350 nm and less, but it would be recognized that the invention has amuch broader range of applicability.

According to one embodiment of the present invention, a compound fornon-linear optics for use at 350 nm and below is provided. The compoundincludes a material for non-linear optics comprising YAl₃B₄O₁₂. Thecompound is free from a molybdenum-bearing impurity of at least 1000parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below comprising a materialfor non-linear optics includes Y_((1-x))M_(x)Al₃B₄O₁₂. x is larger thanor equal to zero and smaller than or equal to 0.1, and M is selectedfrom a group consisting of Sc, La, Yb, and Lu. The compound is free froma molybdenum bearing impurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below comprising a materialfor non-linear optics includes Yb_((1-x))M_(x)Al₃B₄O₁₂. x is larger thanor equal to zero and smaller than or equal to 0.1, and M is selectedfrom a group consisting of Sc, Y, La, and Lu. The compound is free froma molybdenum bearing impurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below comprising a materialfor non-linear optics includes Lu_((1-x))M_(x)Al₃B₄O₁₂. x is larger thanor equal to zero and smaller than or equal to 0.1, and M is selectedfrom a group consisting of Sc, Y, Yb, and La. The compound is free froma molybdenum bearing impurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below comprising a materialfor non-linear optics includes Sc_((1-x))M_(x)Al₃B₄O₁₂. x is larger thanor equal to zero and smaller than or equal to 0.1, and M is selectedfrom a group consisting of Y, La, Yb, and Lu. The compound is free froma molybdenum bearing impurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below comprising a materialfor non-linear optics includes A_(x)M_((1-x))Al₃B₄O₂. x is larger thanor equal to zero and smaller than or equal to 0.1, A is selected from agroup consisting of Sc, Y, La, Yb, and Lu, and M is selected from agroup consisting of Sc, Y, La, Yb, and Lu. The compound is free from amolybdenum bearing impurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a methodfor making a compound for non-linear optics for use at 350 nm and belowincludes providing a plurality of materials. The plurality of materialsincludes a lanthanum bearing compound, and the lanthanum bearingcompound is capable of being decomposed into at least lanthanum oxideupon heating. Additionally, the method includes mixing the plurality ofmaterials to form a mixture based on at least information associatedwith a predetermined proportion, starting a crystallization process inthe mixture to form a crystal, and removing the crystal from themixture, the crystal including lanthanum.

According to yet another embodiment of the present invention, a methodfor making a compound for non-linear optics for use at 350 nm and belowincludes providing a plurality of materials. The plurality of materialsincludes an yttrium bearing compound, and the yttrium bearing compoundis capable of being decomposed into at least yttrium oxide upon heating.Additionally, the method includes mixing the plurality of materials toform a mixture based on at least information associated with apredetermined proportion, starting a crystallization process in themixture to form a crystal, and removing the crystal from the mixture,the crystal including yttrium.

Many benefits are achieved by way of the present invention overconventional techniques. For example, some embodiments of the presentinvention provide new methods of preparation that exclude contaminantsthat preclude the operation of borate huntites in the ultravioletspectrum. In addition, a preparative method has been developed to allowrapid formation of crystal by using an inventive chemical recipe. Suchmethods enable the manufacture of large single crystals of the presentinvention, heretofore unattained in conventional methods. Also, apreparative method has been developed with a lower volatility of thestarting mixture when heated to a melting temperature than conventionalmethods.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and the accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified method for making optical compound according toan embodiment of the present invention;

FIG. 2 is a simplified image for an optical compound according to anembodiment of the present invention;

FIG. 3 is a simplified diagram showing transmission characteristics foran optical compound according to an embodiment of the present invention;

FIG. 4 is a simplified diagram showing frequency conversion by anoptical compound according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates generally to certain compounds havingoptical properties. More particularly, as an example, the inventionprovides a specific compound comprising A_(x)M_((1-x))Al₃B₄O₁₂ for usewith selected wavelengths of electromagnetic radiation. x is larger thanor equal to zero and smaller than or equal to 0.1, A is selected from agroup consisting of Sc, Y, La, Yb, and Lu, and M is selected from agroup consisting of Sc, Y, La, Yb, and Lu. Merely by way of example, thecompound is useful for electromagnetic radiation having a wavelength of350 nm and less, but it would be recognized that the invention has amuch broader range of applicability.

NYAB was developed as a self-doubling crystal, i.e., a crystal that isoptically pumped and generates the fundamental wavelength and its secondharmonic without the need of a separate frequency doubling crystal.However, due to inherent limitations, the possible applications aredrastically limited. First, the fundamental wavelength often can only be1060 nm and 1300 nm. Second, since the crystals usually are only a fewmillimeters in size, they are often not available in adequately largecrystal sizes convenient for commercial use in products.

While NYAB may have been made commercially available from time-to-timein limited quantities, the pure form of YAB has not been commerciallyproduced. The conventional method of production yields small crystalthat contains a significant amount of nonstoichiometric metalscontamination and exhibits substandard crystal quality. Moreover, thefluxing agent(s) used in conventional methods introduce a considerableamount of contaminant that prevents effective device operation in the UVbelow 350 nm.

According to certain embodiments of the present invention, several kindsof borate crystals containing one or more kinds of metal ions of a rareearth metal and the like were prepared, and an occurrence experiment ofdouble harmonic (wavelength: 266 nm) was carried out by irradiatingfrequency doubled Nd:YAG laser (wavelength: 532 nm) onto these boratecrystals. Thereby, the ability to experimentally make NLO materials wasdemonstrated that produce harmonic light below 350 nm. As a result,strong generation of second harmonic 266 nm from borate crystals wasfound that includes both Y and Al, and a novel NLO crystal in the formof yttrium aluminum borate was achieved capable of transmitting andproducing ultraviolet radiation below 350 nm.

It is an object of certain embodiments of the present invention toproduce and utilize nonlinear optical materials that satisfyY_((1-x))M_(x)Al₃B₄O₁₂, where M=Sc, La, Yb, or Lu, and 0≦x≦0.1, andmanufactured by a method that eliminates or significantly reducescontaminants that prohibit device use in the UV spectrum. Morespecifically, some embodiments of the present invention substantiallyexclude metals, such as those of Group 6, from being present in thedevice so as to be useful in the UV below 350 nm.

It is an object of some embodiments of the present invention to providemethods for making nonlinear optical materials that satisfy the abovecomposition without the deleterious UV absorption. One embodimentcomprises forming a mixture comprising from about 10 to about 30 mol %of a source of Y, from about 10 to about 40 mol % of M, from about 15 toabout 40 mol % of a source of Al, and from about 25 to about 50 mol % ofboron oxide. If M is Sc, then the source of M generally is scandiumoxide; if M is La, then the source of M generally is lanthanum oxide; ifM is Yb, then the source of M generally is ytterbium oxide; if M is Lu,then the source of M generally is lutetium oxide. The mixture is heatedto a temperature and for a period of time sufficient to form the NLOmaterial. For instance, the step of heating may comprise heating themixture to a first temperature of at least 850 K, and generally greaterthan about 850 K. The mixture is then cooled. After cooling the mixtureis comminuted (ground to a fine powder, such as by grinding with amortar and pestle), and then heated to a second temperature of at least1300 K, generally greater than about 1300 K.

Another method to form these crystalline materials may be but notlimited to top-seeded solution growth as shown in FIG. 1. The methodincludes the following processes:

-   -   1. High purity oxide powders and chemicals are measured and        mixed in appropriate proportions.    -   2. The mixture is loaded in a crucible and placed in a furnace.    -   3. The mixture is heated and caused to melt into a liquid.    -   4. After a time, melt temperature is brought near to its        freezing point.    -   5. A cold finger material or a seed crystal is introduced to        initiate crystallization.    -   6. Melt temperature and apparatus conditions are modified and        monitored to encourage crystal growth.    -   7. When appropriate, the system is brought down to room        temperature.    -   8. The crystal is removed from the system.

For example, the synthesis of (Y,La)Al₃B₄O₁₂ may be performed asfollows. Yttrium oxide (Y₂O₃), having a purity of greater than 99.9%,lanthanum oxide (La₂O₃), having a purity of greater than 99.9%, aluminumoxide (Al₂O₃), having a purity greater than 99.9%, and boron oxide(B₂O₃), having a purity of greater than 99.9% were purchased fromcommercial vendors such as Aesar and Stanford Materials. A mixture wasformed including about 14 wt % yttrium oxide, about 30 wt % lanthanumoxide, about 19 wt % aluminum oxide, and about 37 wt % boron oxide.

As discussed above, certain embodiments of the present invention isrelated to nonlinear optical (NLO) devices and electrooptic devices andthe ability to employ such devices below 350 nm. Some embodiments of thepresent invention are related to nonlinear optical materials thatsatisfy the general formula Y_((1-x))M_(x)Al₃B₄O₁₂ (M=Sc, La, or Lu and0≦x≦0.1 mol %) and are prepared without contaminants that prevent use inthe ultraviolet (UV) section of the electromagnetic spectrum.

According to some embodiments of the present invention, the nonlinearoptical material Y_((1-x))M_(x)Al₃B₄O₁₂ (M=Sc, La, or Lu, and 0≦x≦0.1)is used for an NLO device for operation below 350 nm. In anotherexample, the nonlinear optical material is used with a laser source fora device that generates optical radiation below 350 nm. In yet anotherexample, the nonlinear optical material is used with a light source fora device that generates optical radiation below 350 nm. In yet anotherexample, the nonlinear optical material is formed in the trigonalcrystal class for use below 350 nm. In yet another example, thenonlinear optical material is formed in the space group R32 for usebelow 350 nm.

In certain embodiments of the present invention, the nonlinear opticalmaterial satisfies Yb_((1-x))M_(x)Al₃B₄O₁₂ (M=Sc, La, or Lu, and0≦x≦0.1) or Lu_((1-x))M_(x)Al₄O₁₂ (M=Sc, La, or Lu, and 0≦x≦0.1). Insome embodiments, the nonlinear optical material Y_((1-x))M_(x)Al₃B₄O₁₂,Yb_((1-x))M_(x)Al₃B₄O₁₂, or Lu_((1-x))M_(x)Al₃B₄O₁₂ is doped by Ceand/or Nd. In certain embodiments, the nonlinear optical materialY_((1-x))M_(x)Al₃B₄O₁₂ or Lu_((1-x))M_(x)Al₃B₄O₁₂ is doped by Ce, Nd,and/or Yb.

As discussed above, while NYAB may be available in limited quantities,the pure form of YAB has not been commercially produced. Theconventional method of production yields small crystal that contains alarge amount of nonstoichiometric metals contamination and exhibitssubstandard crystal quality. Moreover, the solvent used introduces aconsiderable amount of contaminant that prevents device operation in theUV below 350 nm. The summary of work on huntite borates by Leonyuk &Leonyuk (1995) described a flux system that has subsequently remained asa method of producing YAB and its family members, namely the potassiummolybdates K₂MoO₄ and K₂Mo₃O₁₀. Unfortunately, these solventformulations possess severe limitations for large scale crystal growth:a) high flux volatility, b) small crystal yield, and c) significantinclusion of Mo atoms into the target borate huntite structure. Thus,neither has commercial crystal production of pure YAB come about nor hasthe NLO crystal been adopted into laser products.

It is an object of certain embodiments of the present invention toproduce and utilize nonlinear optical materials that satisfyA_(x)M_((1-x))Al₃B₄O₁₂ where 0≦x≦0.1, A=(Sc, Y, La, Yb, Lu), M=(Sc, Y,La, Yb, Lu), and manufactured by a method that eliminates orsignificantly reduces contaminants that prohibit device use in the UVspectrum. More specifically, some embodiments of the present inventionsubstantially exclude metals, such as those of Group 6, from beingpresent in the device so as to be useful in the UV below 350 nm.Avoiding the inclusion of Group 6 impurities, such as Mo, extends the UVtransmission of select borate huntites. In addition, the absence ofsuperfluous metals in the primary crystal composition reduces theoverall bulk spectral absorption over its entire transparency range,such as from 165 to 2700 nm. With the embodiments described herein, theintrinsic transparency may be realized, heretofore unknown anduncharacterized in the scientific community.

As discussed above, it is an object of some embodiments of the presentinvention to provide methods for making nonlinear optical materials thatsatisfy A_(x)M_((1-x))Al₃B₄O₁₂ where 0≦x≦0.1, A=(Sc, Y, La, Yb, Lu),M=(Sc, Y, La, Yb, Lu) without the deleterious UV absorption. Oneembodiment comprises forming a mixture comprising from about 10 to about30 mol % of a source of A, from about 10 to about 40 mol % of M, fromabout 15 to about 40 mol % of a source of Al, and from about 25 to about50 mol % of boron oxide. If A or M is Sc, then the source of A or Mgenerally is scandium oxide; if A or M is Y, then the source of A or Mgenerally is yttrium oxide; if A or M is La, then the source of A or Mgenerally is lanthanum oxide; if A or M is Yb, then the source of A or Mgenerally is ytterbium oxide; if A or M is Lu, then the source of A or Mgenerally is lutetium oxide. The mixture is heated to a temperature andfor a period of time sufficient to form the NLO material. For instance,the step of heating may comprise heating the mixture to a firsttemperature of at least 850 K, and generally greater than about 850 K.The mixture is then cooled. After cooling the mixture is comminuted(ground to a fine powder, such as by grinding with a mortar and pestle),and then heated to a second temperature of at least 1300 K, generallygreater than about 1300 K.

As discussed above, FIG. 1 is a simplified method for making opticalcompound according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The method 100 includes aprocess 110 for measuring and mixing chemicals, a process 120 fortransferring mixture to crucible and furnace, a process 130 for meltingmixture, a process 140 optimizing furnace conditions forcrystallization, a process 150 for introducing seed and startingcrystallization, and a process 160 for cooling system and extractingcrystal. Although the above has been shown using a selected sequence ofprocesses, there can be many alternatives, modifications, andvariations. For example, some of the processes may be expanded and/orcombined. Other processes may be inserted to those noted above.Depending upon the embodiment, the specific sequence of processes may beinterchanged with others replaced. For example, the process 150 ismodified to use spontaneous nucleation, or use conventional opticalcrystal growth procedures to introduce a cold finger to the meltsurface. Further details of these processes are found throughout thepresent specification and more particularly below.

At the process 110, certain chemicals are measured and mixed. Forexample, high purity oxide powders and chemicals are measured and mixedin appropriate proportions. At the process 120, the mixture istransferred to crucible and furnace. For example, the mixture is loadedin a crucible and placed in a furnace. At the process 130, the mixtureis melted. For example, the mixture is heated and caused to melt into aliquid.

At the process 140, furnace conditions are optimized forcrystallization. For example, after a time, the melt temperature isbrought near to its freezing point. At the process 150, a seed isintroduced and the crystallization is started. For example, a seedcrystal is introduced to initiate crystallization. In another example,the process 150 is modified to use a cold finger material to initiatecrystallization. In yet another example, the process 150 is modified touse spontaneous nucleation to initiate crystallization. Additionally,the melt temperature and apparatus conditions are modified and monitoredto encourage crystal growth. At the process 160, the system is cooledand the crystal is extracted. For example, when appropriate, the systemis brought down to room temperature. The crystal is removed from thesystem and ready for tests or further processing.

As an example for the method 100, the synthesis ofY_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1 is performed as follows:

At the process 110, yttrium oxide (Y₂O₃), having a purity of greaterthan 99.9%, lanthanum oxide (La₂O₃), having a purity of greater than99.9%, aluminum oxide (Al₂O₃), having a purity greater than 99.9%, andboron oxide (B₂O₃), having a purity of greater than 99.9% are obtained.For example, these chemicals are acquired from commercial vendors suchas Aesar and Stanford Materials. A mixture is formed including about 14wt % Y₂O₃, about 30 wt % La₂O₃, about 19 wt % Al₂O₃, and about 37 wt %B₂O₃.

At the process 120, the mixture is loaded into a crucible and placed ina high-temperature furnace with atmospheric environment control. Forexample, either ambient or an inert atmosphere is satisfactory. At theprocess 130, the mixture is heated in 12 hours from room temperature toanother temperature ranging from 1450 to 1575 K. The resulting melt isallowed to soak at another temperature for about 1 to 3 days.

At the process 140, the liquid mixture is cooled at a rate of 20 K/hourto a temperature near its freezing point. For example, the temperatureranges from about 1475 to 1400 K. At the temperature, the mixture isheld for about 8 hours. At the process 150, by spontaneous nucleation,or by using conventional optical crystal growth procedures to introducea crystalline seed or cold finger to the melt surface, the productbegins to form while cooling to a final temperature of 1300 K at a rateof about 1-5 K/day. Additionally, during the course of the growth, themelt temperature and apparatus conditions are monitored and optionallymodified to encourage crystal growth, either by an operator and/or bythe automated control system on the furnace.

At the process 160, the system is then cooled to room temperature at acooling rate of about 50 K/hour. Colorless, transparent crystal ofY_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, is obtained and removed from thefurnace.

In yet another example for the method 100, the synthesis ofLu_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, is performed as follows:

At the process 110, lutetium oxide (Lu₂O₃), having a purity of greaterthan 99.9%, lanthanum oxide (La₂O₃), having a purity of greater than99.9%, aluminum oxide (Al₂O₃), having a purity greater than 99.9%, andboron oxide (B₂O₃), having a purity of greater than 99.9% are obtained.For example, these chemicals are acquired from commercial vendors suchas Aesar and Stanford Materials. A mixture is formed including about 21wt % Lu₂O₃, about 30 wt % La₂O₃, about 16 wt % Al₂O₃, and about 34 wt %B₂O₃.

At the process 120, the mixture is loaded into a crucible and placed ina high-temperature furnace with atmospheric environment control ofnitrogen with a partial pressure of oxygen, which is larger than orequal to 3000 ppm. At the process 130, the mixture is heated in 12 hoursfrom room temperature to another temperature ranging from 1450 to 1575K. The resulting melt is allowed to soak at another temperature forabout 1 to 3 days.

At the process 140, the liquid mixture is cooled at a rate of 20 K/hourto a temperature near its freezing point. For example, the temperatureranges from about 1475 to 1400 K. At the temperature, the mixture isheld for about 8 hours. At the process 150, by spontaneous nucleation,or by using conventional optical crystal growth procedures to introducea crystalline seed or cold finger to the melt surface, the productbegins to form while cooling to a final temperature of 1275 K at a rateof about 1-5 K/day. Additionally, during the course of the growth, themelt temperature and apparatus conditions are monitored and optionallymodified to encourage crystal growth, either by an operator and/or bythe automated control system on the furnace.

At the process 160, the system is then cooled to room temperature at acooling rate of about 50 K/hour. Colorless, transparent crystal ofLu_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, is obtained and removed fromthe furnace.

In yet another example for the method 100, the synthesis ofSc_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, is performed as follows:

At the process 110, scandium oxide (Sc₂O₃), having a purity of greaterthan 99.9%, lanthanum oxide (La₂O₃), having a purity of greater than99.9%, aluminum oxide (Al₂O₃), having a purity greater than 99.9%, andboron oxide (B₂O₃), having a purity of greater than 99.9% are obtained.For example, these chemicals are acquired from commercial vendors suchas Aesar and Stanford Materials. A mixture is formed including about 8wt % Sc₂O₃, about 34 wt % La₂O₃, about 18 wt % Al₂O₃, and about 39 wt %B₂O₃.

At the process 120, the mixture is loaded into a crucible and placed ina high-temperature furnace with atmospheric environment control. Forexample, either ambient or a nitrogen atmosphere is satisfactory. At theprocess 130, the mixture is heated in 12 hours from room temperature toanother temperature ranging from 1475 to 1600 K. The resulting melt isallowed to soak at temperature for about 1 to 3 days.

At the process 140, the liquid mixture is cooled at a rate of 20 K/hourto a temperature near its freezing point. For example, the temperatureranges from about 1500 to 1425 K. At the temperature, the mixture isheld for about 8 hours. At the process 150, by spontaneous nucleation,or by using conventional optical crystal growth procedures to introducea crystalline seed or cold finger to the melt surface, the productbegins to form while cooling to a final temperature of 1300 K at a rateof about 1-5 K/day. Additionally, during the course of the growth, themelt temperature and apparatus conditions are monitored and optionallymodified to encourage crystal growth, either by an operator and/or bythe automated control system on the furnace.

At the process 160, the system is then cooled to room temperature at acooling rate of about 50 K/hour. Colorless, transparent crystal ofSc_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, is obtained and removed fromthe furnace.

FIG. 2 is a simplified image for an optical compound according to anembodiment of the present invention. This diagram is merely an example,which should not unduly limit the scope of the claims. One of ordinaryskill in the art would recognize many variations, alternatives, andmodifications. The optical compound includes Y_(x)La_(y)Al₃B₄O₁₂, where0≦x, 0≦y, and x+y≦1, made by the method 100 as discussed above. Thesynthesis starts with yttrium oxide (Y₂O₃), lanthanum oxide (La₂O₃),aluminum oxide (Al₂O₃), and boron oxide (B₂O₃). As shown in FIG. 2, the6×6×7 mm crystal is sufficiently large and possessesoptically-transparent faces that enable it to function in laser lightmodification device.

FIG. 3 is a simplified diagram showing transmission characteristics foran optical compound according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. The optical compoundincludes Y_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, made by the method 100as discussed above. The synthesis starts with yttrium oxide (Y₂O₃),lanthanum oxide (La₂O₃), aluminum oxide (Al₂O₃), and boron oxide (B₂O₃).As shown in FIG. 3, a curve 300 shows the transmission percentage as afunction of wavelength. The transmission percentage remains relativeconstant from 350 nm to about 175 nm.

FIG. 4 is a simplified diagram showing frequency conversion by anoptical compound according to an embodiment of the present invention.This diagram is merely an example, which should not unduly limit thescope of the claims. One of ordinary skill in the art would recognizemany variations, alternatives, and modifications. The optical compoundincludes Y_((1-x))La_(x)Al₃B₄O₁₂, where 0≦x≦0.1, made by the method 100as discussed above. The synthesis starts with yttrium oxide (Y₂O₃),lanthanum oxide (La₂O₃), aluminum oxide (Al₂O₃), and boron oxide (B₂O₃).For example, the optical compound is the crystal as shown in FIG. 2.During the experiment, laser pulses with a wavelength of about 532 nmwere delivered to a 6-mm-by-6-mm-by-7-mm Y_((1-x))La_(x)Al₃B₄O₁₂crystal. In response, the crystal output a light beam received by animaging scintillator card, which was sensitive to ultraviolet radiation.As shown in FIG. 4, an image was taken using a camera that was madeblind to 532 nm with a filter for the photograph. In the image, bluefluorescence was observed on the imaging scintillator card. Henceultraviolet light was generated by the Y_((1-x))La_(x)Al₃B₄O₁₂ crystalthrough a SHG process and was detected by the imaging scintillator card.In another experiment, a dichroic mirror was specifically optimized for266-nm light transmission and placed between the Y_((1-x))La_(x)Al₃B₄O₁₂crystal and the imaging scintillator card. Blue fluorescence, which issimilar to that in FIG. 4, was also observed. Hence ultraviolet light at266 nm was generated by the Y_((1-x))La_(x)Al₃B₄O₁₂ crystal.

As discussed above, and further emphasized here, the method can be usedto make various types of optical compounds. According to one embodimentof the present invention, a compound for non-linear optics for use at350 nm and below is made by the method 100. The compound includes amaterial for non-linear optics comprising YAl₃B₄O₁₂. The compound isfree from a molybdenum bearing impurity of at least 1000 parts permillion. According to yet another embodiment of the present invention, acompound for non-linear optics for use at 350 nm and below is made bythe method 100. The compound comprising a material for non-linear opticsincludes Y_((1-x))M_(x)Al₃B₄O₁₂. x is larger than or equal to zero andsmaller than or equal to 0.1, and M is selected from a group consistingof Sc, La, Yb, and Lu. The compound is free from a molybdenum bearingimpurity of at least 1000 parts per million.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below is made by the method100. The compound comprising a material for non-linear optics includesYb_((1-x))M_(x)Al₃B₄O₁₂. x is larger than or equal to zero and smallerthan or equal to 0.1, and M is selected from a group consisting of Sc,Y, La, and Lu. The compound is free from a molybdenum bearing impurityof at least 1000 parts per million. According to yet another embodimentof the present invention, a compound for non-linear optics for use at350 nm and below is made by the method 100. The compound comprising amaterial for non-linear optics includes Lu_((1-x))M_(x)Al₃B₄O₁₂. x islarger than or equal to zero and smaller than or equal to 0.1, and M isselected from a group consisting of Sc, Y, Yb, and La. The compound isfree from a molybdenum bearing impurity of at least 1000 parts permillion. According to yet another embodiment of the present invention, acompound for non-linear optics for use at 350 nm and below comprising amaterial for non-linear optics includes Sc_((1-x))M_(x)Al₃B₄O₁₂. x islarger than or equal to zero and smaller than or equal to 0.1, and M isselected from a group consisting of Y, La, Yb, and Lu. The compound isfree from a molybdenum bearing impurity of at least 1000 parts permillion.

According to yet another embodiment of the present invention, a compoundfor non-linear optics for use at 350 nm and below is made by the method100. The compound comprising a material for non-linear optics includesA_(x)M_((1-x))Al₃B₄O₁₂. x is larger than or equal to zero and smallerthan or equal to 0.1, A is selected from a group consisting of Sc, Y,La, Yb, and Lu, and M is selected from a group consisting of Sc, Y, La,Yb, and Lu. The compound is free from a molybdenum bearing impurity ofat least 1000 parts per million. In one embodiment, M includes at leastone selected from a group consisting of La, Lu, Sc, Y, and Yb. Inanother embodiment, A includes at least one selected from a groupconsisting of Sc, Y, La, Yb, and Lu.

As discussed above, according to certain embodiments, each of varioustypes of optical compounds made by the method 100 is free from amolybdenum bearing impurity of at least 1000 parts per million. Forexample, the compound is free from a molybdenum bearing impurity of atleast 500 parts per million. In another example, the compound is freefrom a molybdenum bearing impurity of at least 100 parts per million. Inyet another example, the compound is free from a molybdenum bearingimpurity of at least 10 parts per million. In yet another example, thecompound is free from a molybdenum bearing impurity of at least 1 partper million. In yet another example, the compound is substantially freefrom a molybdenum bearing impurity. According to some embodiments of thepresent invention, each of various types of optical compounds made bythe method 100 each is free from any impurity of at least 1000 parts permillion that can prevent the compound from being used for non-linearoptics at 350 nm and below. For example, the compound is free from anysuch impurity of at least 500 parts per million. In another example, thecompound is free from any such impurity of at least 100 parts permillion. In yet another example, the compound is free from any suchimpurity of at least 10 parts per million. In yet another example, thecompound is free from any such impurity of at least 1 part per million.In yet another example, the compound is substantially free from any suchimpurity.

As discussed above, according to certain embodiments, each of varioustypes of optical compounds made by the method 100 has a volume greaterthan about 0.001 mm³. For example, the compound has a volume greaterthan about 0.01 mm³. In another example, the compound has a volumegreater than about 0.1 mm³. In yet another example, the compound has avolume greater than about 1 mm³.

According to some embodiments, various types of optical compounds madeby the method 100 can be used for non-linear optics at 350 nm and below.For example, the use is associated with a wavelength ranging from about350 nanometers to 160 nm. In another example, the use is associated witha wavelength ranging from about 350 nm to 170 nm. In yet anotherexample, the use is associated with a device that generates opticalradiation below 350 nm. In yet another example, the device comprises anNLO system, the compound associated with a laser system, and/or thecompound associated with a light source.

According to certain embodiments, the method 100 can be used to make acompound for non-linear optics for use at 350 nm and below. For example,the compound is associated with the trigonal crystal class for use below350 nm, and/or the space group R32 for use below 350 nm. In anotherexample, the compound also includes dopant including at least oneselected from a group consisting of Ce, Nd, and Yb. In one embodiment,the nonlinear optical material includes NYAB. In another embodiment, thenonlinear optical material includes Yb:YAB. In yet another embodiment,the nonlinear optical material includes Ce:YAB.

According to yet another embodiment of the present invention, a methodfor making a compound for non-linear optics for use at 350 nm and belowincludes providing a plurality of materials. The plurality of materialsincludes a lanthanum bearing compound, and the lanthanum bearingcompound is capable of being decomposed into at least lanthanum oxideupon heating. Additionally, the method includes mixing the plurality ofmaterials to form a mixture based on at least information associatedwith a predetermined proportion, starting a crystallization process inthe mixture to form a crystal, and removing the crystal from themixture, the crystal including lanthanum. For example, the plurality ofmaterials comprises lanthanum oxide. In another example, the pluralityof material further comprises boron oxide. In yet another example, themethod further includes placing the mixture into a furnace. In yetanother example, the method further includes heating the mixture to afirst predetermined temperature, and cooling the mixture to a secondpredetermined temperature. In yet another example, the starting acrystallization process comprises inserting a crystalline seed to a meltsurface. In yet another example, the crystal includesA_(x)M_((1-x))Al₃B₄O₁₂. x is larger than or equal to zero and smallerthan or equal to 0.1, A is selected from a group consisting of Sc, Y,La, Yb, and Lu, and M is selected from a group consisting of Sc, Y, La,Yb, and Lu. In yet another example, the method is implemented accordingto the method 100.

According to yet another embodiment of the present invention, a methodfor making a compound for non-linear optics for use at 350 nm and belowincludes providing a plurality of materials. The plurality of materialsincludes an yttrium bearing compound, and the yttrium bearing compoundis capable of being decomposed into at least yttrium oxide upon heating.Additionally, the method includes mixing the plurality of materials toform a mixture based on at least information associated with apredetermined proportion, starting a crystallization process in themixture to form a crystal, and removing the crystal from the mixture,the crystal including yttrium. For example, the plurality of materialsincludes yttrium oxide. In another example, the plurality of materialfurther includes boron oxide. In yet another example, the method furtherincludes placing the mixture into a furnace. In yet another example, themethod further includes heating the mixture to a first predeterminedtemperature, and cooling the mixture to a second predeterminedtemperature. In yet another example, the starting a crystallizationprocess comprises inserting a crystalline seed to a melt surface. In yetanother example, the crystal includes A_(x)M_((1-x))Al₃B₄O₁₂. x islarger than or equal to zero and smaller than or equal to 0.1, A isselected from a group consisting of Sc, Y, La, Yb, and Lu, and M isselected from a group consisting of Sc, Y, La, Yb, and Lu. In yetanother example, the method is implemented according to the method 100.

It is understood the examples and embodiments described herein are forillustrative purposes only and that various modifications or changes inlight thereof will be suggested to persons skilled in the art and are tobe included within the spirit and purview of this application and scopeof the appended claims.

1. A non-linear optical material comprising a YAl₃B₄O₁₂ crystal; whereinthe material contains less than 1000 parts per million of a molybdenumbearing impurity and is capable of generating ultraviolet light at 266nm.
 2. The material of claim 1 wherein the material contains less than500 parts per million of a molybdenum bearing impurity.
 3. The materialof claim 2 wherein the material contains less than 100 parts per millionof a molybdenum bearing impurity.
 4. The material of claim 3 wherein thematerial contains less than 10 parts per million of a molybdenum bearingimpurity.
 5. The material of claim 4 wherein the material contains lessthan 1 part per million of a molybdenum bearing impurity.
 6. Thematerial of claim 5 wherein the material is substantially free from amolybdenum bearing impurity.
 7. The material of claim 1 wherein theultraviolet light comprises laser light.
 8. The material of claim 1wherein the material is associated with the trigonal crystal class foruse below 350 nm.
 9. The material of claim 1 wherein the material isassociated with the space group R32 for use below 350 nm.
 10. Thematerial of claim 1, and further comprising a dopant including at leastone selected from a group consisting of Ce, Nd, and Yb.
 11. The materialof claim 10 wherein the material comprises NdYAB.
 12. The material ofclaim 10 wherein the material comprises Yb:YAB.
 13. The material ofclaim 10 wherein the material comprises Ce:YAB.
 14. The material ofclaim 1 wherein the material contains less than 1000 parts per millionof a lead bearing impurity.
 15. The material of claim 14 wherein thematerial contains less than 500 parts per million of a molybdenumbearing impurity.
 16. The material of claim 15 wherein the materialcontains less than 100 parts per million of a molybdenum bearingimpurity.
 17. The material of claim 16 wherein the material containsless than 10 parts per million of a molybdenum bearing impurity.
 18. Thematerial of claim 17 wherein the material contains less than 1 part permillion of a molybdenum bearing impurity.
 19. The material of claim 18wherein the material is substantially free from a molybdenum bearingimpurity.